1. Field of the Invention
This invention relates to apparatus for reliably detecting and monitoring the temperature of brain tissue, particularly of a neonatal patient, while also monitoring the oxygenation of that patient's blood hemoglobin.
2. Background Information
During pediatric cardiac surgery, it is usually necessary to obtain circulatory arrest so that no blood is flowing in the patient's blood vessels. In order to minimize the likelihood of injury to the patient's organs, particularly the brain, the patient is covered with a cooling blanket which reduces the patient's core temperature by hypothermic cooling prior to the actual surgery. During surgery, the patient's heart is stopped and the intent is to maintain a brain temperature in the range of 15-18° C. Operating time is normally between 15 and 30 minutes. If the surgical procedure extends beyond that time, the infant's chances of survival decrease.
During the operation, since the patient's heart is stopped, there is no longer cold blood circulating through the blood vessels of the brain. To prevent the patient's head being warmed by the ambient air of the operating room, during circulatory arrest, brain cooling is usually augmented by a cooling cap placed on the patient's head while a cooling fluid is circulated through the cap to maintain the desired brain temperature. Thus the hypothermic cooling in combination with temperature monitoring not only controls brain temperature but also controls the rate of cooling of the brain, as well as the rate to re-warm it.
In addition, during cardiac surgery, the oxygenation of the patient's hemoglobin is often monitored by an oximeter because the patient will not thrive with inadequate oxygenation. For this, a cerebral oxygen saturation sensor, in the form an adhesive strip, may be placed across the patient's forehead. A sensor such as this is available from Somanetics Corporation of Troy, Mich. The sensor includes a light source, usually a light-emitting diode (LED), which produces infrared wavelengths. Light from the sensor is passed across the patient's forehead from one side of the strip to a receiver, e.g., a photodiode, on the other side of the strip. The light that is not absorbed by the blood-perfused regional tissue under the sensor is picked up by the receiver. The absorbance of the infrared light differs significantly between the oxygen-bound (bright red) and oxygen-unbound (dark red) blood hemoglobin in the regional tissue. Therefore, the oxy/deoxy hemoglobin ratio, i.e., the regional oxygen saturation value (r SO2), can be calculated and displayed. If the value is too low, steps may be taken to remedy that situation, e.g., by postponing the surgery or speeding up the surgery to restore blood circulation.
There has recently been developed an intracranial temperature detection apparatus designed especially for neonatal patients. It uses microwave radiometry to monitor intracranial temperature at depth and usually also near surface (skin) temperature thus enabling close control over the hypothermia process; see U.S. Pat. No. 8,062,228, the entire contents of which is hereby incorporated herein by reference. That apparatus employs a microwave transducer designed to be positioned on the neonate's forehead. However, if the patient is wearing a cooling cap as described above, there is no room to apply to the infant's forehead both the transducer and the aforesaid oxygen saturation sensor.
Accordingly, there is a need to provide apparatus that can monitor intracranial temperature at depth and desirably also near surface temperature, as well as oxygenation of blood hemoglobin all at the same time using a single transducer able to be affixed to a neonate's forehead even though that patient may be wearing a cooling cap.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.